Bone morphogenetic protein-2 enhances osteoclast formation mediated by interleukin-1 alpha through upregulation of osteoclast differentiation factor and cyclooxygenase-2

Bone morphogenic protein-2 (BMP-2) is a member of the transforming growth f actor beta (TGF-beta) superfamily, While BMP-2 is capable of inducing bone formation ectopically, little is known about its role on osteoclastogenesis . In this study, we examined the effect of BMP-2 on osteoclast-like multinu cleated cell (OCL) formation in cocultures of osteoblast-like cells and hem atopoietic cells of bone marrow origin. BMP-2 alone did not stimulate OCL f ormation in this culture system; however, it strongly enhanced OCL formatio n in a dose-dependent fashion in the presence of interleukin-1 alpha (IL-1 alpha). Western blot analysis showed that a simultaneous addition of BMP-2 and IL-1 alpha synergistically enhanced cyclooxygenase-2 (COX-2) expression in osteoblast-like cells. Moreover, Northern blot analysis revealed that t he level of osteoclast differentiation factor (ODF) mRNA increased by treat ment with BMP-2 and IL-1 alpha in osteoblast-like cells. It is noted that B MP-2 alone did cause an increase in the expression of both COX-2 and ODF ge nes. The stimulatory effect of BMP-2 was abolished by adding nonsteroidal a nti-inflammatory drugs, such as indomethacin and a selective COX-2 inhibito r NS-398. Addition of NS-398 inhibited the expression of the ODF gene in os teoblast-like cells treated with BMP-2 and IL-1 alpha. These results indica ted that the combination of BMP-2 and IL-1 alpha stimulated osteoblast-like cells to elevate the expression of both COX-2 and ODF genes, resulting in an enhanced OCL formation. Since BMP-2 alone induced the expression of COX- 2 and ODF genes in osteoblast-like cells, it appears to be one of the regul ating factors of osteoclastogenesis, (C) 1999 Academic Press.